1. Technical Field
The present invention relates to an actuator, an optical scanner, and an image forming apparatus.
2. Related Art
It is known that an actuator configured with a torsional oscillator is used as, for example, an optical scanner for a laser printer producing images by optical beam scanning. For example, Japanese laid-open patent application number 2005-181395 (JP-A-2005-181395) discloses one such actuator.
The actuator disclosed in JP-A-2005-181395 contains a frame-shaped support board, a flat-plate-shaped mirror (reflection mirror) disposed inside the support board, and a linear bar-shaped torsion bar connecting the support board and the mirror. According to this structure, the mirror rotates in accordance with the twisting of the torsion bar. Optical beam scanning can be performed by the rotation of the mirror. This type of actuator has been developed as a compact device, but to the contrary, the size of the mirror included in the actuator is increasing.
According to the actuator disclosed in JP-A-2005-181395, assuming that the size of the actuator does not change in a plan view, the length of the torsion bar decreases as the area (diameter) of the mirror increases. In this case, the torsion bar does not easily twist and therefore it is difficult to produce sufficient rotation of the mirror for the light beam scanning.